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Does static longitudinal stability require download on the tail?
After having encountered this meme too often for comfort, I ask myself today in order to have the possibility to explain the issue in detail.

Where is the meme?

@DavidDeVine: That static longitudinal stability would require download on the tail, as the question says.

No, static longitudinal stability does not necessarily imply a download on the tail.

Static longitudinal stability requires that the Centre of Gravity is in front of the Centre of Lift, indicated as n.p.$_{fixed}$ in the drawing. Only then will an increase in Angle of Attack d$\alpha$ result in an opposing pitching moment: if d$\alpha$ > 0 then $dC_N$ > 0, resulting in a higher lift force. The neutral point must be behind the CoG in order to transform the higher lift into a nose down moment. Note that the drawing shows a longitudinally stable situation with a positive lift on the horizontal tail.

+1 Yes, Might I add, that it is this simple. "Static longitudinal stability requires that the Centre of Gravity is in front of the Centre of Lift". It can be the case that this can happen with two airfoils generating positive, (upwards) lift, one in front of the CG, producing a nose up pitch moment, and one behind the CG producing nose down pitch moment,  (and this is the case for a canard-design), but in conventional (elevator at tail) aircraft, this is not the normal condition.

Why? I believe ACs are determined using the same math as are CGs. Imagine x is the Wing Lift Moment arm, and y is the Tail(elevator) lift moment arm. W is wing lift and T is tail Lift. Then for the overall Aerodynamic center (AC) or Center of Lift, to be behind the CG, Ty  must be greater than Wx. Ty > Wx  <=> T/W > x/y. The Tail lift to Wing Lift ratio must exceed the Wing Moment arm to Tail moment arm ratio. True in a canard, where T is always > than W. Possible in a conventional aircraft (x very small, or a large T), but this would not be normal design.

It's a bit questionable if you ask me, it depends on your definition of stable. The answer is completely correct, both configurations can be stable during normal operation, only when you have a download on the stabilizer, it is also stable when the flow around the stabilizer is disturbed at very high angles of attack. Configurations with upward stabilizer force will almost certainly crash in that case.

@rickboender Yes indeed! In calm and well defined conditions a positive tail load can be statically stable. However the neutral lift point has a nasty tendency to shift forward in adverse circumstances, like when in a sideslip there is partial loss of lift of the tailplane. Only when the aircraft is trimmed with a negative tailplane load can stability be guaranteed in all circumstances. Definitely during start and landing at higher angles of attack. However, during fast cruise, does the tailplane ever experience a vertical gust strong enough to stall it? The velocity triangle says no.

For the impatient reader: The answer is no.
Let me explain it in detail. For this, it is helpful to simplify things as much as possible and then add the complications step by step so I can explain what each changes.
The simplest layout uses a symmetric airfoil for both wing and tail and arranges both in the same plane and without a difference in incidence. If this arrangement is moved through the air at the subsonic speed $\text{v}_\infty$, the graphical representation in side view would look like this:

Both produce only friction drag and no lift. Now we add some angle of attack, in the next picture I chose 5°:

Now both create some lift (green arrows) in proportion to their size. The loading per area is the same for wing and tail - both have the same angle of attack and the same flow conditions, after all. Also, the local lift can bee summed up in the quarter point of the respective chord in both cases.
But that is too simple! Lift is created by deflecting air downwards, so the above picture is strictly possible only for wings of infinite aspect ratio. Therefore, the next picture shows the same arrangement with some downwash angle added behind the wing, so the angle of attack on the tail is reduced by $\alpha_{\text{d}}$ = 2° in this example:

This still leaves a positive local angle of attack on the tail (the downwash angle is quite a bit smaller than the wing's angle of attack, counted up from the zero-lift angle, for most regular airplanes), so the tail lift is still positive. In order to be trimmed at this angle of attack, the center of gravity needs to be between both lift vectors at a location proportional to the ratio between the two lift vectors.
But now a change in the angle of attack will change the local lift of both surfaces in proportion to the angle change. The result is an indifferent behavior towards changes in angle of attack. Flyable, but rather stressful. So we need to add a lower incidence at the tail in order to achieve static longitudinal stability:

Now the angle of attack on the tail is reduced by another 2°, and only a very small but still positive lift vector remains on the tail. The center of gravity needs to be shifted forward, very close to the quarter point of the wing to trim the aircraft.
A difference in the angle of incidences of only 2° is rather small, so we increase that to -5°, and now we indeed get a download on the tail:

If we now increase the angle of attack to 10° because we want to fly more slowly, we get more lift on the tail, right? The result should look like this:

With double the angle of attack on the wing the downwash angle doubles as well, but since the tail sees the same angle increase, its lift will turn positive, doesn't it?
Wrong again! The center of gravity has not changed, and in this configuration the tail has more lift than what is required for trimmed flight. And it better should - this is a stable configuration, after all, and an imbalance must result in order to create the nose-down moment required for stability.
A trimmed configuration needs to deflect the elevator to trim the new angle of attack. Since the lift on the main wing can be summed up in the same point in both angle of attack cases, the lift on the tail must be equal to the earlier trim case, like this:

This insight can be generalized: For airplanes with symmetric airfoils (like aerobatic airplanes) the lift force on the tail at trimmed level flight will be the same, regardless of speed. For that reason, a wing airfoil with a low travel of its center of pressure will require the smallest possible tail surface for a given wing surface in order to be trimmed at all speeds. This reasoning drove Willy Messerschmitt to pick the NACA 2R1 for most of his fighter designs and even the Me-321 cargo glider.
But for regular aircraft, a cambered airfoil is more common. Now we remove the last simplification and camber the wing airfoil. Below I adjusted the airfoil shape, but not it's incidence, so the now negative zero-lift angle will result in a larger effective difference in the angle of incidences. Whereas the zero-lift angle of the symmetric airfoil before was at zero degree, the cambered airfoil has a negative zero-lift angle of attack. Would the symmetric airfoil be mounted at the same effective angle of attack, its incidence would be higher. The tail incidence of -2° from case 4 can be reused here:

Now the downwash angle is higher, because the cambered wing produces more lift at the same geometric angle of attack, and the lift vector on the tail is negative again. The lift vector on the wing has shifted back due to camber (the lift vector of the symmetric airfoil is still plotted in light green), so the center of gravity is now ahead of the wing's center of pressure.
But in all the last cases the lift on the tail is negative, isn't it? Does that mean that the lift on the tail is negative in all cases?
No, it doesn't. Again we increase the angle of attack to 10°, but whereas the tail lift did not change when a symmetric airfoil was used on the wing, the cambered airfoil experiences a forward shift in the center of pressure when the angle of attack is increased. Consequently, even in the trimmed case now the tail lift will change to a positive value again!

Note that the elevator is again deflected in order to trim the new angle of attack. Even though, the lift has crossed into positive values again. Not much, but a high lift on the tail should be avoided anyway. Not only should sufficient margin remain for control inputs, but also because lift on the tail is more expensive in terms of drag.
Conclusion: A stable configuration can be achieved with positive lift on the tail, at least at high angle of attack.

so the now negative zero-lift angle will result in a larger effective difference in the angle of incidence This is due to the shift in center of lift?

Now the downwash angle is higher and the lift vector on the tail is negative again. Why is the downwash angle higher?

@TomMcW: First question: No, but due to camber which means that the same geometric angle of attack produces a higher effective angle of attack (which is measured between the zero-lift angle and the geometric angle). Second question: At the same geometric angle of attack the cambered wing has more lift and, consequently, more downwash.

Static stability: what is the direction of the pitching moment upon a change in angle of attack due to a gust, does the change in pitching moment counteract the change in AoA or does it tend to amplify it? That is clearly always the case when CoG is in front of centre of lift. I cannot see how the forward shift in lift of a cambered airfoil helps with a stabilising pitching moment.

@Koyovis: The travel of the center of pressure of a positively cambered airfoil destabilizes the aircraft. But if the tail is big enough, overall stability is the same as with a symmetric airfoil and a smaller tail.

In another answer it was stated:
"... Lift is created by deflecting air downwards, so the above picture is strictly possible only for wings of infinite aspect ratio. Therefore... "
I politely demur.  Any airframe, no matter the aspect ratio of the wing (or tailplane), will generate positive lift on both surfaces if the angle of attack is increased to a sufficiently positive value. This does not imply that this configuration would be stable.
As to downwash, yes there is downwash, but the downwash at the tailplane is very dependent on the position of the tailplane relative to the wing. In some aircraft, where the tailplane is mounted high up (a T-tail) the downwash is significantly less than the downwash when placed in a lower position (although, because of obvious effects, the downwash effect inceases as AOA increases - in fact this is what caused the infamous "pitch-up" issue in the McDonnell Douglas F-101 Voodoo, because of it's T-tail, and is the main reason for the anhedral on the F-4 Phantom horizontal stabilator).
To assume that the change in AOA at the tailplane due to downwash from the wing is a standard, calculable value independent of wing AOA, speed, G-loading, or placement of the tailplane is not a valid assumption.
Next, the issue of static stability is not explicitly addressed. Discussing the scenario of two different stable situations both of which are at 1-G level flight, but just at different AOAs and speeds, does not address what would happen if AOA was increased at the same speed.
When we talk about static stability, a common mistake is often made. We discuss overall static stability, as qualitatively measured by the magnitude of the static margin (the distance between the OVERALL aerodynamic center and the CG), but then, in diagrams, we draw separate vectors displaying the Force on the wing and the force on the tailplane. The total aerodynamic center is the combined effect of all aerodynamic forces on the airframe from all surfaces, not just the wing. and because the tailplane is so much further from the CG than the wing. it's effect moves the AC further aft than the green vectors in Mr Kampfs diagrams. To get to a situation where the total Aerodynamic center of pressure is ahead of the CG, requires that the wing Lift (the forward green arrow,) be much further ahead of the CG Than is depicted. This is why the configurations above are not stable. The Wing Lift has a Significantly higher nose up pitching moment from AOA increase disturbances than the  nose down pitching moment from increases in positive lift from the tail plane.
Just look at video showing F-16 out of control for an illustration.
But just thinking about the definition of AC tells  us all we need to know. The AC is defined as the point within the aircraft, that All lift can be treated as acting through for the purposes of calculating pitch moments.
So if this point (the AC), is ahead of the CG, then it is by definition unstable, because it's pitch moment (from the effects of all lift, from both wings and tailplane), is in the same direction as any disturbance. Just as shooting an arrow backwards would be.
The only way this configuration can be stable is if the total AC remains behind the CG. Aircraft with elevator controls in front (canards) can accomplish this because the Wing, which produces the bulk of the lift, is behind the CG, and canard (in front of the CG) produces significantly less lift. So the total AC remains aft of the CG. In a conventional aircraft, where the main wing is ahead of the elevator control surface, this is not easily possible. If the main wing is behind the CG, then it will produce a nose down pitch moment, and the tailPlane must generate negative lift to balance pitch moments. If the main wing is far enough forward of the CG to put the overall AC also ahead of the CG, its Nose up pitching moment will (by definition, since the AC is ahead of the CG), be greater than the opposing pitching moment from the tailplane.  The only way this configuration can be stable is if the Main wing AC is only slightly forward of the CG, but not far enough forward to place the overall AC in front of the CG. Designing an aircraft so that these attributes remain in this narrow band is problematic, and so, I believe, is not the normal aircraft design approach.
All discussion above about the effects of the camber on the airfoils are irrelevant. Regardless of the camber, or downwash, There is still a total aerodynamic center, through which all forces can be considered to act through for the purposes of calculating pitch moments (and by implication static longitudinal stability). and if this AC Is ahead of the CG, the aircraft is statically unstable, and will fly out of control unless the stability is augmented by other mechanisms (like FBW).

It is, however, theoretically possible to suspend the CG between the fuselage/wing and horizontal tail individual ACs (both creating positive lift) in a way that total aircraft AC is still behind the CG. The above would require a very narrow CG band to achieve this, but it is theoretically possible and the configuration would be stable.

@Cpt Reynolds, yes - theoretically possible, but unlikely, (I believe you would have to do the actual math calculations to establish the conditions that would make this possible), but this scenario would be very unusual and not a common arrangement. Clearly, an aircraft using a canard configuration can be designed this way. so although without doing the actual math, I can't be certain, I think that some value of the ratio between the wing area of the forward airfoil and the rearward airfoil might be a threshold beyond which this condition is possible.

Also, to make it absolutely clear as to what the disagreement is here, (I hope this is accurate, as positions sometimes change as clarity develops), I am not saying this is impossible, I am only saying that in conventionally designed aircraft (where the pitch control surface is at the tail), this is not the case. What I arguing against is the idea that it is always the case that the tail is generating positive (upwards) lift, and that it is false that reducing static margin or relaxing positive stability  will reduce drag & increase range/endurance performance. This is what I am refuting.

Mate - some of what you say has validity, but please leave out the negativity and the rants.

@Koyovis,  I apologize if I have created the impression of a "rant", or negativity. I do not mean that sarcastically. I know my passion sometimes creates inaccurate impressions about my intent. None of it is anything more than passion about the topic and frustration when I feel I am failing to communicate successfully. And, thank you for apparently reading my comments with enough thoughtfulness and open-mindedness to recognize some of what I am saying.


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What are the "beta lines" of a gas turbine engine component?
For a compressor in particular, what do the beta lines represent? I know for a compressor map you have the lines of constant spool speed, and the contours of isentropic efficiency. I also understand the purpose of the surge line and how it acts as a limit for stable compressor operation. I'm not entirely sure what beta lines do though, are they just fractions of the pressure to mass flow ratio that results in surging? Or are they something else?

Beta lines are either linear or parabolic shaped lines that are conveniently placed and spaced between the surge line and the choke line of the compressor (or fan) characteristic (also known as compressor/fan map). Such lines are also found in the turbine characteristics maps.
Basically, the Beta lines create a new axis system that prevent a solver from finding multiple (or the incorrect) operating point(s). The lines itself do not represent anything, they are simply added for convenience and calculation stability.
Compressor maps describe the relation between various parameters which are based on experiments or CFD calculations; corrected mass flow, pressure ratio, spool speed and efficiency. In gas turbine performance simulation, a new operating point needs to be found for a change in operating condition. Knowing that speed lines can contain a local maximum pressure, you cannot uniquely describe an operating point with a pressure and a speed, there can be 2 solutions for corrected mass flow. Hence, gas turbine performance engineers have created the concept of an alternative coordinate system that prevents that multiple solutions can be found; this is very useful when programmatically finding/iterating the new operating point.
Compressor maps typically are 2-in, 3-out parameter maps, to find the 3-out parameters (pressure ratio, efficiency and corrected mass flow) you require a unique pair of Beta and spool speed values.

Compressor map (Beta lines are hidden):

Compressor map (linear Beta lines are shown):

Example of parabolic Beta lines:

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What is baro corrected altitude?
I have data from an aircraft which I am trying to understand. One column contains the baro corrected altitude (in ft, e.g. 256) and another the pressure altitude(also in ft, e.g. -44). The two example data points given were measured at the same time.
I have issues finding a definition of the baro corrected altitude. How is it defined and how does it differ from e.g. pressure altitude or other types of altitudes?

A baro corrected altimeter is corrected for variations in local pressure and altitude.  You will find the altimeter should read field elevation when the altimeter setting is correctly entered (within 75 feet).

Although, I can not find an FAA reference for baro corrected altitude, my understanding is that baro corrected altitude is the Indicated Altitude on a pressure sensitive altimeter when the Kollsman Window is set to the correct current barometric pressure. This may be different than the Indicated Altitude on a non-adjustable/settable altimeter. It may also be different than the Indicated Altitude on a pressure sensitive altimeter set for a non-current altimeter setting.
In contrast, Pressure Altitude is the height above the standard datum plain set at an altitude where the barometric pressure is 29.92 inches of Mercury. You would get Indicated Altitude to match Pressure Altitude by setting the altimeter Kollsman Window to 29.92 inches of Mercury. 5is may not represent the height above Mean Sea Level.
True Altitude is the height above the 19 year average Mean Sea Level. It is consistent regardless of barometric pressure, temperature, humidity, geographic location, etc.
Pressure Altitude is the True Altitude adjusted for non-standard barometric pressure. Indicated Altitude may differ from True Altitude based on what barometric pressure (if ant) is used to calibrate the altimeter. Having to use an altimeter setting from a weather observation (ATIS) not located at the field of use or one that has not yet updated to current.

Pressure altitude isn't height above anything, it is altitude at which current static pressure would be expected under international standard atmosphere conditions. Due to effects of temperature 1000 ft of pressure altitude may correspond to less geometric height when it is cold or more when it is warm, so it does not match geometric height above the 1013.25 hPa isobar most of the time.

@JanHudec - Per the Airplane Flying Handbook, “Pressure altitude is the height above the standard datum 29.8 112 plane (SDP). The aircraft altimeter is essentially a sensitive barometer calibrated to indicate altitude in the standard 29.92 0 atmosphere. If the altimeter is set for 29.92 "Hg SDP, the altitude indicated is the pressure altitude—the altitude in the standard atmosphere corresponding to the sensed pressure.”

@JanHudec - “The SDP is a theoretical level at which the pressure of the 30.5 atmosphere is 29.92 "Hg and the weight of air is 14.7 psi. As atmospheric pressure changes, the SDP may be below, at, or above sea level. Pressure altitude is important as a basis for determining aircraft performance, as well as for assigning flight levels to aircraft operating at above 18,000 feet.”

@JanHudec - What you have described is Density Altitude which is Pressure Altitude adjusted for non-standard temperature.

An aircraft altimeter is essentially a sensitive barometer, which is exactly the reason pressure altitude is the pressure expressed as altitude in ISA. The instrument only measures pressure, so it can only indicate pressure. The “SDP” is superfluous. You have pressure, so you have to find the point in ISA where it occurs and subtract that height from your current position to find SDP… but you already found the height, so you just call it your pressure altitude and don't need to bother even defining the SDP.

More importantly, the “SDP” is not well defined for the whole air column. If two aircraft are flying at FL060, that is 6,000 ft pressure altitude, and FL120, that is 12,000 ft pressure altitude, but it's very, very cold, they may easily be only 5,000 ft apart. That means the “SDP” for the first is 1,000 ft higher than “SDP” for the other. Such definition is pointless (there is, unfortunately a bunch of pointless things in the Airplane Flying Handbook).

Density altitude is a different thing. Density altitude is the density expressed as altitude in ISA where that density is expected. It can be calculated from pressure altitude and temperature, but it is not a pressure altitude corrected for temperature, it is a different thing.

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What is the CLmax of the CF-100 Canuck?
I've been struggling to find specifications for the CF-100 Canuck. What is the CLmax of the CF-100 Canuck and how can I find it?

The CF-100 had a symmetrical NACA 0010 airfoil, which had a Clmax of just under 1.4. according to Airfoil Tools.com (Xfoil).  Is that what you are looking for?

Yeah that's perfect thank you!


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Does the auto thrust at takeoff compensate for asymmetric engine characteristics?
When a percentage thrust has been determined for take off the auto thrust system (Airbus) or the auto throttle (Boeing) will send the data to the engines FADECs to provide the required thrust.
When the levers are set at FLEX (Airbus) or when the levers push button is pressed (Boeing) the engines will develop the takeoff thrust which is displayed as an N1 or as an EPR.
It seems the FADECs will command the same N1 (EPR) for all engines since the displayed N1 (EPR) are the same for both (all) engines. Am I right?
Considering the engines may have different age and therefore producing different thrusts for the same indicated N1 (EPR), a thrust assymetry will result. Is it true? How this is acceptable at take off?
Considering the engines total running hours (aging of the engine) are known by the operator, is there a way  to enter such a data to the auto thrust or to the auto throttle or to the FMS in order to get at take off really equal thrusts and not just equal N1(EPR)?

N1 is not the same as EPR. N1 is RPM whereas EPR is Engine Pressure Ratio, calculated as Turbine Outlet Pressure / Compressor Inlet Pressure. EPR can be used as an accurate indicator of thrust regardless of the age of the engine (assuming the sensors work correctly), whereas N1 cannot.

Thank you, so let us concentrate on N1  with respect to the question. Further if I understand well your answer it means both engines will deliver very similar thrust all the time, but from one day to another the power will depend on atmospheric conditions. Thank you.

N1 doesn't really say anything about thrust, just how fast the low pressure compressor wheel is turning. If two engines of the same model but different years of manufacture, cycles and hours are producing the same EPR under the same atmospheric conditions, the thrust produced is the same. What I don't know is if and how FADEC takes that into consideration. I would assume it is one of the sensors it is looking at, but don't know for sure at the moment. That is why I did not make my comment an answer.

Considering a GE engine (N1) It would sound very strange to get difference of thrust at take off with engines of different age, the trouble is that the indicated N1s are similar at take off, as far as I know.


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Where to get information on FAA AIXM 5.0 versions of Special Activity Airpace (SAA) files?
Does anybody know where to find documentation or someone to ask questions about the SAA database provided by the National Flight Data Center? I have some questions about the ambiguity of some of the data.
Or better yet, is there a better source for the boundaries and meta data for special-use airspace?

I guess you may ask the National Flight Data Centerwhich publishes the data. Email for NFDC Support Desk is here.

They have a support desk? Cool. Didn't think to look for that.

Actually, the link you gave just takes me to the login page. But I'll poke around...

The second link gives you the email of the NFDC support desk (below the login fields). I do not publish the email here due to spam possibility.

d'oh! I see it now. I thought I needed to log in first.

Mins, The fellow at the help desk was very nice and sent me the document I needed to finish my product. Thank you. Make your comment an answer and I'll mark it accepted.

I'm glad you got your documentation. I'll write an answer, that can help other readers. Thanks a lot for having taken the time to provide a feedback to the community.

One possibility is to contact the FAA National Flight Data Center (NFDC). They provide information as part of the US Aeronautical Information Services (AIS).
NFDC Support Desk email is available on this login page, below the login data boxes.
See also this question: Where to find a waypoints/fixed points, navaids, airports database for other aeronautical data sets in case you need them too.

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What are the common private pilot practices for helicopter off-airport landing in US?
These questions address the legal aspects of off-airport landing and basically conclude that the relevant laws and regulations are very fragmented.
Aside from the legal aspects, what are common practices and habits in terms of off-airport landing in US for private pilots? Are there clearly identified "off-airport-landing-friendly" states or regions where this is commonly practised?
As a comparison, in Switzerland, off-airport landings are nearly systematically practised by private helicopter pilots. In France, you need an easy-to-obtain authorisation and then make a few calls for each occurence/location, but it is an otherwise rather common practice. In Germany, off-airport landing is a big no go for private pilots. How do things fare in US?

In many "back-woods" areas throughout the country it is perfectly legal to land an aircraft as long as you have the land owners permission, or the permission of the controlling agency. Alaska is a great example of this where a significant portion of air operations are off-airport. A lot of it boils down to the same regulations as using ATV's, as in do no harm and have permission.

Indeed, most of the time, you can land, as long as the owner approves. The tricky part might be the insurance: landing in a 'non FAA approved' location may void your insurance, so if you roll the helicopter after landing on a slope you did not know how to handle, you might have to pay for it yourself (if you survive it that is).

There are minimum altitudes for cruise flight but altitude may be reduced below these minimums as needed for approach to landing. I don't know of any FAA regulation that requires landing at a designated airport(or heliport)
Title 14(aerospace) of the federal code of regulations part 91.119 (part 91 is general flight rules for all aircraft) simple says that;
"Except when necessary for takeoff and landing, no person may operate an aircraft below the following altitudes:"
A: Anywhere. At an altitude as to create an "undue hazard" to people and property on the ground in the event the engine fails. (Will you hit a building or dense crowd, or will you have time to aim for an open spot?)
B: Over any congested area of a city or open air assembly of people, below an altitude of 1000feet above the highest obstacle within 2000 foot horizontal radius from the aircraft.
C: over other than congested areas, no less than 500 feet above the surface, except for over water or sparsely populated areas. In those areas the aircraft may not be operated within 500 feet in any direction from buildings or boats. So no actual minimum altitude limit if you are over a field 500feet to the side of a barn.
D:Helicopters, powered parachutes, and weight-shift controlled aircraft(hang gliders and ultralights), if conducted without hazard to person or property o the surface may be operated at less than the minimums prescribed in B and C, provided the operator of a helicopter complies with any special routes or altitudes specifically prescribed by the FAA.(Generally special provisions are only found in high air traffic areas near major airports or over high security areas.)
These are paraphrased slightly for clarification and because I type how I likes to type, but the actual wording of the law is very close.
There may also be some local laws about noise limits if operations are frequent but this is not limited to aircraft.

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How to calculate your landing ground roll distance with this chart?

Under these conditions:  Pressure altitude  5,000 ft, Headwind  Calm, Temperature   101 F
I have no idea how to even start

Hi @Matt item 2 is going to be important in your scenario.

Yes, read the fine print and apply to 5000 feet, 41F + 60F.  If possible,  land on a 2000 foot runway, just to be sure.

All else being equal, increased temperature increases density altitude, and thus true airspeed for a given indicated/calibrated airspeed. Increased landing speed will increase the landing roll distance.
In your exercise above, the primary relevant condition given is a runway at 5000'. This tells you which column of the table you'll be using, i.e. the one labeled "At 5000 feet & 41 °F". Note that the temperature given there is the "standard" temperature for that altitude.
But there are footnotes. The first footnote, discussing headwind, doesn't apply because there's no headwind. But the second one, discussing temperature does. Your given temperature is 101 °F, which is 60 °F higher than standard temperature for the given altitude of 5000'. The footnote says you need to add 10% to the distance for every 60 °F higher than standard, and there is exactly 60 °F higher temperature given in the conditions, so you need to add 10%.
The standard ground roll is 495', so adding 10% to that you get 544.5' (which you might round to 545').
Note that if the temperature was, for example, only 30 °F higher, that doesn't mean you can ignore the second footnote. You should interpolate based on the information there, adding 5% in that example to the landing roll instead of 10%. Likewise a temperature 90 °F higher would require increasing the landing roll figure by 15% (assuming you think it's even safe to operate the airplane at that temperature! at 131 °F, there are lots of other problems that might argue against flying at all, including failure of paved surfaces, overheating of the engine, pilot dehydration and fatigue, etc.)
You don't say whether the runway is unpaved. The table you're using assumes a "hard surface runway". If it's a grass runway, you'd also want to apply the third footnote. Note that the footnote there is for a "dry, grass runway". A grass runway that's wet, or a gravel runway, or a snowy/icy runway could produce different results. A wet, grass runway in particular could reduce the landing roll significantly, while an icy paved runway could increase it significantly, as compared to "standard" conditions. A gravel runway might perform very similarly to a hard surface, depending on the condition.
In other words, while it's clear from the round numbers (5000' is exactly the base altitude for the column you'll use from the table, while the 101 °F temperature is exactly one unit of the 60 °F difference used for the second footnote) that this is just an academic exercise, in the real world you may have other factors to take into account, including the pilot's skill in maintaining the required approach speed of 60 mph (an even slightly faster approach can greatly increase the ground roll) and in using the brakes at their maximum effectiveness, and of course the condition of the airplane itself, especially the tires and brakes, along with the various environmental factors mentioned in the table and those I mentioned above.

Wouldn't a wet grassy surface be more slippery? I would assume a longer ground run in that case. Anyway, nice answer!

@PeterKämpf: "Wouldn't a wet grassy surface be more slippery?" -- the answer is a simple "it depends". You're right...slippery grass can make landing rollout longer, even as takeoff runs are also increased. See e.g. https://aviation.stackexchange.com/questions/49295/why-is-the-landing-distance-increased-on-grass-runways. On the other hand, wet grass is often longer and the ground underneath softer, which creates more drag and will decrease the landing rollout. But you can't count on it...you won't know until you've been on the runway. Hence my use of the word "could", rather than "will".


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Can cabin pressure be lower than outside pressure?
In order to allow adaption to changed pressure, the pressure change in an aircraft cabin is stretched out over time. My observation is that the cabin pressure drops even before the plane takes off, and has not yet reached ground level at the time the aircraft lands. This would make sense, allowing for longer adaption times, but needs better sealing which is able to work both ways.
My question to the systems specialists: Can an aircraft cabin have a lower pressure than outside, and is the technique of stretching out the pressure change as explained above actually used?

I wonder if modern day hulls can even support a negative pressure diff. Most of them are built on the assumption that outside press is equal or several psi below internal

Here's what happens if it is ... youtu.be/Zz95_VvTxZM or youtu.be/JsoE4F2Pb20

Besides the sealing the aircraft would also need a vacuum pump that is able to pull air out of the cabin which means extra weight.
The way aircraft maintain cabin pressure is through a air cycle machine that pushes air into the aircraft and outflow valves. There is no facility to pull air out of the craft.
Any pressure drop you may experience on the ground is probably because the pilot increases air pressure on the ground slightly to test the seals and then releases it before takeoff.

To create a lower pressure is easy with an eductor pump. Bleed air will provide the energy, and the performance is easily sufficient to suck a little air out of the cabin. The mass of eductor pumps is really low. After all, the pressure drop should only be slight - I do not want to create a vacuum. There is really no such means for regulating pressure?

@PeterKämpf Why would there be such a mechanism? The only reason that planes need to be pressurized is that humans are feeble and can't cope with low pressure. All you need to solve that problem is a mechanism to increase the pressure if it gets too low. The outside air pressure is never too high for passenger comfort or safety, so why would you need a mechanism to lower cabin pressure below external atmospheric?

@DavidRicherby: In order to stretch out the time for the pressure change. Rapid pressure change is uncomfortable; humans need to adapt even if the change is only 0.3 bar.

@PeterKämpf and the time is already stretched, planes don't go to 8k ft and then keep cabin pressure stable,

@PeterKämpf as mentioned, the time of pressure change is already stretched.  In the EMB145 the cabin is maintained at departure elevation for the first 10 minutes or so, then climbed at ~500 fpm or less until reaching 8k cabin altitude at cruise and ~7.8 dPSI.  On descent the cabin will descent at ~400 fpm over the course of the descent.   The cabin pressure change schedule is independent of the actual aircraft climb and descent rates (except where max delta PSI is limiting, but the scheduling is smart enough that this isnt really an issue).

The A320 family as well as the B737NG series of aircraft start to pressurize during the takeoff roll. The cabin pressure is increased by about 0.1 Psi as this makes pressure changes on the outflow valve during the roll and the rotation less noticeable.
Only during a descent with the outflow valve closed, the cabin pressure could become lower than the ambient pressure. To prevent damage due excessive under pressure aircraft are fitted with inflow valves that open automatically if the pressure differential exceeds a threshold.

Can an aircraft cabin have a lower pressure than outside

Yes, absolutely is CAN.  It's not desirable, but if the seals are all tight enough & you descend quickly enough, it can happen.  Because the effects on the structure would be bad, aircraft typically have a negative pressure relief valve to prevent this from happening.  By definition, you don't need to prevent something that can't happen, so yes, a negative pressure differential is possible.
What you want to avoid, and with modern pressurization controllers, you probably can't reach, is a situation where you descend quickly enough to "catch the cabin" and the cabin altitude matches the aircraft altitude.  (Which is to say, you're depressurized -- with or without the negative pressure relief valve opening -- a few thousand feet above the ground.)  At that point (assuming you're still descending quickly), the cabin rate goes from something mild, a couple hundred feet-per-minute, to something much greater, perhaps a couple thousand feet-per-minute.  If you aren't used to dealing with that sort of a rate of change, it is disconcerting & uncomfortable, and for somebody who is flying with a minor head cold who could keep up with a gentle rate of change, it could be pretty painful.  And since nobody wants to scare Grandma, this is undesirable!
Thankfully, with modern pressurization controllers, you probably won't ever get there -- they'll manage the rate to keep things on schedule regardless.  With an older analog controller, it's possible, although probably pretty rare.
As explained in other answers, the modern controllers start to pressurize so that the cabin altitude goes slightly below the airport elevation (i.e. the cabin pressure rises slightly) at some point before liftoff (when throttles are first advanced, typically -- it's all automatic).  And on landing the cabin is likewise slightly pressurized, and that pressure bleeds off slowly after you have weight-on-wheels.  This is done so that the system transitions into and out of pressurization gradually, instead of immediately upon liftoff or on landing.  The outflow valve moving at full speed can give you a pretty good "pop," and that's not comfortable, so gradual transitions are designed in.
It's all about keeping the paying passengers comfortable & happy!

No aircraft is capable of reducing pressure below ambient - that would require pumps going the other way, and there's zero reasons to do it. Your observation of the cabin pressure dropping is an illusion, probably the pressure increasing a small amount as the pressurization system comes online.
It is conceivable that an aircraft could have a negative pressure differential on descent. If it descends very quickly it could have in internal pressure of 8,000 feet (normal cruise pressure) but be below that altitude. The difference would not last long, but it does take time to pump up a widebody - a fully pressurized 747 holds an extra ton of air, engines are at idle and the outflow valve (inflow in this case) isn't all that big.


text:
What does AO2A in the remarks of a METAR mean?
I am familiar with AO2 in the METAR remarks as described in this answer, which means the station is automated and has a precipitation discriminator.  I have noticed sometimes there is AO2A in the remarks now as in this METAR:
KBAD 171406Z 17012KT 10SM OVC004 18/17 A3002 RMK AO2A SLP168
How is AO2A different from AO2?  I assume it is probably some additional capability.

AO2 Automated station without manual augmentation
AO2A Automated station with manual augmentation.

That means this is an automated station but some elements have been added manually.

15.13.4
Supplementary remarks may be included in observations from US stations following the identifier group RMK.
These data are intended as national interest only and are equivalent to Section 5 of FM 12 SYNOP.

Observations
from automated stations shall have one of the following contractions as the first entry following RMK:
AO2 Automated station without manual augmentation;
AO2A Automated station with manual augmentation.

Source WMO Manual on codes.


text:
Difference between Mountain Breeze/Katabatic Winds and Valley Breeze/Anabatic Winds
I am studying Meteorology for my CPL exams, and taking EASA's 2020 Learning Objectives as a guideline for the topics I have to study.
In the topic of local winds, there are subtopics for Anabatic & Katabatic Winds and Mountain & Valley Winds (050.02.04.01.01 and 050.02.04.01.02 in the screenshot below).

The book I am primarily using does not mention anything about Mountain & Valley winds and I have searched the internet and the only thing closer to the Mountain and Valley Winds I could find were the Mountain and Valley Breezes, which I am assuming refer to the same phenomenon.
The problem, however is that some resources say that Mountain Breeze and Katabatic Winds are the same:

...however, some online resources categorically say that they are different, but no further explanation is provided except that Anabatic and Katabatic Winds are on much larger scale than Valley and Mountain Winds:

The origin of Anabatic and Valley winds are similar:

Slope of hill warms up due to more direct insolation to mountain side than the valley floor, leading to air on the slope being warmer and less dense than the air in the valley. Air on the mountain slope rises up and cold air in the valley replaces the rising air

Similarly, the formation mechanism for Katabatic Winds and Mountain Winds are also similar:

At night the ground will cool more quickly and becomes colder than the air above. Air in contact with the ground cools.  This now denser air slides downslope and moves into the valleys.

So my question is What makes Anabatic and Katabatic Winds differ from Valley and Mountain Winds? Since their formation mechanisms are the same, what makes Anabatic and Katabatic larger and stronger?
P.S. I realize that the resources that I have shared are not very reliable and can contain inaccurate information. However, I couldn't find any reliable resource which dealt with and compared both phenomenons

There's an interesting write up on valley winds here: https://xcmag.com/paragliding-techniques-paramotoring-skills/forecasting-valley-winds/

Be aware there is also https://earthscience.stackexchange.com

Under the right conditions-- i.e. with the right large-scale meteorological forcing-- the wind can blow up or down a slope -- causing an associated cooling or heating effect-- independent of any diurnal cycle.  E.g. the famous downslope "Santa Ana" winds, or "Chinook" winds.  Note that in these cases, the air is being warmed by its descent, so much that a person in the valley below will feel an increase in temperature when the wind arrives.
In the case of diurnal mountain/valley breezes or winds, the air is warmed by the sun (or cooled by radiation due to lack of sunlight) and then moves up or down the slope accordingly.  If you stood in a valley in the mountains in the evening and felt the temperature of the evening downslope breeze (or wind), you'd likely feel a drop in temperature, not a rise, because the air entering the valley from above would be air that had lost heat through radiation somewhere higher up on the slope, and then moved down the slope.  Even though the air would experience some amount of katabatic warming during its descent down the slope, it would still likely feel like a cool wind, displacing warmer air from the valley.  In the case of diurnal breezes or winds where there is no larger-scale meteorological forcing, if the descending air experienced katabatic warming such that it was no longer cooler and and denser than the air it was encountering  on it its downslope journey, it would lose its impetus to continue downslope, and the breeze or wind would tend to come to an end or at least disperse in altitude so that it was no longer concentrated near the ground.  If there is larger-scale meteorological forcing, the downslope winds can continue even in conditions where they are causing the temperature in the valley below to increase, not decrease. They can also continue day and night, independent of the diurnal cycle.
But the highlighted content in your source is confusing, because it tends to suggest that predictable daily upslope/ downslope (mountain/ valley) effects  should not be described as anabatic/ katabatic phenomena.  Fundamentally, "anabatic" and "katabatic" just mean "upslope" and "downslope".  They don't pertain to why the air is moving up or down the slope.

I do not agree with the answer by quiet flyer. I especially do not agree with the conclusion "Fundamentally, "anabatic" and "katabatic" just mean "upslope" and "downslope". They don't pertain to why the air is moving up or down the slope."
Anabatic and katabatic winds are thermally induced winds, (with katabatic sometimes also used for other downslope winds) with the mechanisms similar to a land/see breeze, but also involving a sloping terrain. The classical explanation involves the Bjerknes circulation theorem and can be found in textbooks.
The AMS glossary:

anabatic wind
In mountain meteorology, an upslope wind driven by heating (usually daytime insolation) at the slope surface under
fair-weather conditions. ...
In general usage, this term does not
suffer from the multiplicity of meanings that katabatic wind does.

katabatic wind

Most widely used in mountain meteorology to denote a downslope flow driven by cooling at the slope surface during periods of light larger-scale winds; the nocturnal component of the along-slope wind systems.

Occasionally used in a more general sense to describe cold air flowing down a slope or incline on any of a variety of scales, including phenomena such as the bora, in addition to thermally forced flows as described above.

Still in the second general sense it is still a cold heavy air. Not just any downslope wind. The bora gets its strength from the stable stratification and from the heavy cold air rushing down after overcoming the mountain ridge, albeit it was forced to overcome it dynamically.

The mountain and valley and slope winds specifically:
These are thermally induced winds in a specific environment. They can be explained by density differences arising in the horizontal direction due to mountain slopes being heated during the day and cooled during night. This causes a density difference in comparison with the air at the same altitude far from the mountain. The physical mechanism is similar to the mechanism causing the land and the sea breeze and the vorticity generation can be explained by the Bjerknes circulation theorem. (An interesting  historical perspective at Thorpe et al., BAMS 2003.
The mechanism is quite general, but the nomenclature distinguishes:

the land and the sea breeze - mostly horizontal across the shore. The density difference arises due to higher sensible heat fluxes over land.

the slope winds - along sloped surface. The density difference arises due to the slope surface being heated and cooled by radiation (solar shortwave and own thermal longwave)

the mountain and the valley winds - or the mountain-valley wind systems
These happen on a larger scale, not just along a single slope but on the scale of a whole mountain range. The air heated close to the surface by solar radiation rises from the valleys during the day and the air cooled by the surface infra-red radiation descends from the mountains during the night.

The main difference between the terms anabatic/katabatic vs. mountain/valley is the specificity of the term. The mountain and valley winds are more specific terms describing specific examples of anabatic and katabatic winds.

Interesting answer, and likely the best one. I was going in part off the actual derivation of the words. But does not your answer imply that the some of the source material in the question itself was incorrect? For example the original source material quoted by the OP implied that anabatic and katabatic winds were a different phenomenon that mountain/valley winds.  Another source quoted by the OP stated that anabatic and katabatic winds were "larger and stronger" than mountain/ valley winds.  I take it you would disagree with all this?  Might be worth incorporating into answer.

@quietflyer I should probably address this. Anabatic and katabatic are more general terms than mountain/valley winds.

When I was younger I used to wonder why they even bothered to draw "dry fronts" on the map out in Texas and why they were so important.
Just as cold air is denser than warm air, dry air is denser than humid air (at the same temperature).
The misconception here seems to be description of local and larger weather phenomena, behaving the same way for different reasons.
Locally, the ground absorbs heat from the sun$^1$ better than air during the day, resulting in upslope winds during the day.  At night, the ground radiates its heat and becomes colder than the air (except for a layer near it), resulting in a downslope flow of wind.  Because this is a local phenomena, there are not any great changes in humidity.  Anabatic and katabatic winds are strictly driven by temperature differences.
On a larger scale, winds driven up over higher terrain have moisture wrung out of them by forming clouds and rain.  This "dry" air can descend into valleys by the exact same mechanism: higher density.  Being of larger scale, winds such as the Chinook can reach hurricane strength, whereas local winds are more like "breezes".
According to this reference downslope winds created by differences in humidity are not "true" katabatic winds. (Even though temperature and humidity differences both cause wind, and combinations of cold/dry and warm/humid produce the strongest effects).  Curiously, the California's Santa Ana wind is considered a "katabatic" wind, but, coming off the desert, one might wonder where its moisture went?
$^1$ much of the solar radiation reaching the earth is in the Infrared
wavelengths, along with visible light

authors: Vladimir F Героям слава


text:
How does deploying full flaps affect Takeoff run and distance?
There is a question in EASA Question Bank (AviationExam) that asks:

How will the takeoff distance change if the flaps are increased from 0 to full?
(a) Reduce (this is marked as correct since many student have reported this option as being correct from their exams)
(b) Increase
(c) No Change
(d) Reduce until medium setting, then increase

My understanding was that after 15/20$^{\circ}$ further flaps deployment is only for increasing drag and slowing down the aircraft.
Here is an excerpt from CAE Oxford Principles of Flight Book:

Take-off distance depends upon unstick speed and rate of acceleration
to that speed.
a) Lowest unstick speed will be possible at the highest CLMAX and this will be achieved at a large flap angle
b) But large flap angles also give high drag, which will reduce
acceleration and increase the distance required to accelerate to unstick speed.
c) A lower flap angle will give a higher unstick speed but better acceleration, and so give a shorter distance to unstick.
After take-off, a minimum climb gradient is required in the take-off configuration. Climb gradient is reduced by flap, so if climb gradient is limiting, a lesser flap angle may be selected even though it gives a longer take-off distance

The above (TOR and TOD both increase) seems to contradict the answer EASA considers correct...
This question is similar to Should full flaps be deployed on takeoff? and accepted answer is more or less saying what the oxford book is saying. So my question is:
Is there any scenario or plausible logic that might make EASA answer correct for even a single corner case?

D was obviously the answer intended by whoever originally composed the question.  But, that's not a full answer to the question you are actually asking here--

There are very often errors in question banks used by online study guides - I've seen this reported time and time again over the years from student pilots on various online forums. D is quite obviously the correct answer.

Also (not surprisingly), the question is ambiguous.  In option D, in the phrase "and then increase", is that simply supposed to mean a progressive increase with each extra degree of flap, compared to with one degree less flap?  Or does that mean that the takeoff distance actually becomes greater than with zero flap?  If the latter, that statement is obviously false if the flaps are deployed only slightly more (say one degree more (say one degree more) than the setting that gives the min. takeoff length, and arguably in some aircraft designs (ctd)

(ctd) and arguably in some aircraft designs (say with limited total flap availability, e.g. later-model Ces 152 w/ 30 degrees max flap available)  might even be true in some conditions (e.g. muddy field) even with full flaps.  So depending on how we read the question, an argument can be made that in some cases option A could be the best answer.

It depends on the $C_l$ an zero flaps and that at full flaps along with many other variables such as engine thrust, their propulsive efficiency and even $C_d$ just to name a few. So the correct answer is going to vary from aircraft to aircraft - there is no correct answer. However, option D seems to be true for most aircraft.

@757toga I don't think any do. However, the shortest possible takeoff distance is obtained by starting the run with zero flaps, and then selecting full flaps during the run such that full flaps are achieved at rotation speed. So surely, there are conditions where full flaps is the best candidate for minimum takeoff distance.

@757toga What you just described is precisely why full flaps are not used for takeoff - the small (if any) improvement in takeoff performance simply does not outweigh the dramatic reduction in climb performance. Also, I certainly would not recommend you to try this either; in fact, I would recommend you to use the minimum necessary flaps for the given runway length, since doing so maximizes the climb performance and leaves you with a higher airspeed - ideal in case the engine quits. Good day!

Is there any scenario or plausible logic that might make EASA answer [meaning answer A]
correct for even a single corner case?

Yes-- consider a Cessna 152 with 30 degrees maximum flaps available, on a soft muddy field, with no wind.  The takeoff distance will be less with full flaps than with no flaps.
The takeoff distance might be slightly less with less flaps-- say 20 or 25 degrees flaps-- than with 30 degrees flaps, but that would not be inconsistent with answer A still being correct for this particular case.
Answer D is arguably a good answer too, depending on how we read it-- it's not clear whether the phrase "and then increase" is supposed to mean "and then becomes larger than the takeoff distance with zero flaps", or is supposed to mean "and then becomes larger than the takeoff distance with somewhat less flaps."  If we understand the answer to mean the latter, then "D" is arguably the best answer, because it would be true for nearly all aircraft in nearly all situations, unless the flap travel is extremely limited-- after the flaps have been deployed to some optimum value, further deployment will usually start to increase the takeoff distance again, even in the case of a soft field, etc.  In contrast, if we read the phrase "and then increase" to mean "and then becomes larger than the takeoff distance with zero flaps", then this is true most of the time, but it's not difficult to think of exceptions, e.g. the case described in the paragraph immediately above.
It seems almost certain that answer "D" was intended to be the correct answer.

Thanks. I am quite sure exam questions are supposed to be for general or common situations, and if the examiner had soft field TO with C-152 example in mind, he would have specified.
Who ever wrote that question probably had option D in mind but somehow it got messed up when fed into QB. Several students had reported option A as correct answer by EASA, so I am quite certain the problem exist in EASA QB and AvExam has replicated that issue in their own QB.

Yes, (d) would seem far and away the best answer unless:
The aircraft had a very high thrust to weight ratio.  Then (a) is also a possibility.
It is very important to know the limitations of each type of aircraft.
The strategy for lift-off in as short a distance as possible is to generate adequate lift from improving Coefficient of Lift and airspeed, which factors in as V$^2$.
Thrust vs drag and mass are the deciding factors.
An aircraft with a very low thrust to weight ratio, such as a powered glider, benefits from keeping drag low and even more from a rolling start.
Lift-off airspeed difference flaps up and down may be as little as 5 knots.
A more powerful aircraft, such as a C-130 J transport, with prop blast under the wing and plenty of thrust to move, might do better with flaps down.
It is important to remember that flaps increase the AoA of the part of the wing where they are deployed. Climbs with flaps can be done with the nose lower to the horizon as long as an altitude gain is seen.  Slats and flaps can add more camber to the wing without significantly changing local AoA.
Reducing takeoff distance with full flaps only is rare.  However, a soft field take off$^1$, where the ground surface adds to the drag, may favor a higher flap setting.
$^1$ as suggested in comments


text:
do you have to go to the air force to be a commercial pilot
do you have to go to the air force to be a commercial pilot

No, you do not.

Which country are you asking about?

Please don't open new accounts to repeat a question.  It won't work here.  Instead, edit your existing question or ask for clarification on the answers given.


text:
Why are autonomous vehicles not used at airports for on-ground services?
Autonomous vehicles have been around for over an decade, other industries such as the maritime industry have already been using unmanned vehicles at ports. Curious to know why airports are reluctant to implement this despite the clear benefits it has.

Most vehicles need a person to do something when they reach their destination. Move luggage or catering, hook up fuel or lavatory service, etc. So that person might as well drive the vehicle there. There is work on systems for towing planes though.

Until there is a good, accurate way of tracking all aircraft on the ground, autonomous vehicles racing around moving airplanes is probably not going to happen. ADS-B is helping us get there, but we aren't there yet.

Could you clarify what the clear benefits are?  Most questions of "why not...?" on this site are based on numerous assumptions, some unwarranted, and it's easier to analyze and critique a very specific proposal and list of assumed benefits rather than our guess of what the design and its benefits would be.

@CodyP Humans are expensive and prone to errors, especially with repetitive tasks. There's a good reason maritime ports have already embraced autonomous driving.

Many of the ground vehicles need to have a trained human to make it useful for the plane (for example the fuel truck, mobile stairs, ...) so it makes sense for it to cart the trained human around. If you do that you may as well make said human drive. This means there is a high ratio of human controlled vehicles mixed with the autonomous vehicles. There are also the firetrucks that need priority, giving it to them sometimes needs human intuition in where you stop or move to to make a path.
You don't want the vehicle to path underneath an airplane and cause damage, or potentially end up in the jetblast.
Someone needs to monitor them and coordinate with the ground controller whenever they need to access/cross the taxiways.

Autonomous vehicles are great, but they do not fit to an airport. It would be too complicated to develop vehicles that fit into the environment of an airport.
Airplanes are very sensitive. If something gets damaged, the plane needs to stay on ground.
For the pushback it would be maybe possible. But again, many sensors and supervision by a human is needed.

Frankfurt Airport is currently testing two autonomous busses from french company Navya. While during the first test run they are only to be used by employes, future tests near the active runways might follow.
Unfortunately, most articles on that are in German, but I found one in English here.

Full autonomy is still in it's infancy. The consequences of an autonomous vehicle malfunctioning and crashing into an airliner fully loaded with both people and fuel are... a lot worse than an autonomous vehicle malfunctioning and crashing into the side of a ship.
Same can be said for one that goes haywire and wanders out onto a runway that has airliners on final approach or taking off.

Most likely because autonomous vehicles are brand new; Google and other companies are in the process of perfecting the technology just for regular street use.  I suppose as time goes by more ground vehicles are going to be automated, including ones at airports.

The port of Rotterdam has had automated ground vehicles since at least 1993. Automated driving is well established in industrial applications (the key difference being a well-defined environment, unlike the chaos of public roads)

So it is.........


text:
What are fuel biases?
Does anyone have an idea of what is it? From what I gathered from the web, it seems that this is the margin of error between the actual, real fuel consumption of the aircraft and the fuel consumption recorded in the aircraft systems (FMC?). I read that the system only estimates the fuel consumption via the fuel flow, which has some degree of inaccuracy.
Airbus and Boeing seemed to have different terms for this, PERF Factor, Fuel factor. The seem to be close in definition but I'm not really sure.

Are you looking for accuracy of metering (difference between metered fuel flow vs actual fuel flow) or accuracy of consumption prediction (difference between actual consumption and fuel planning)?

You should give more context. Where can you find this expression ("fuel biases")?

Sorry for giving scarce details. It's supposed to be part of IATA's guidance on Fuel Efficiency / Conservation practices. I've only heard about it, but not have actually read the material, and was just asking around what it is.  Net research yielded a comparison between the calculated consumption by the aircraft's computer vs the flight plan, so I  asked if that was it.  But I think it affects the resulting fuel load duriing flight planning, the same way as degradation from the airframe and engine does.


text:
What is the necessity of Obstacle Departure Procedure(ODP)?
What is the necessity of Obstacle Departure Procedure(ODP)?
Standard Instrument Departure(SID) is enough, isn't it?

This question is closely related, but it doesn't address the difference between an ODP and a SID so I don't think it's an exact dupe

Departure procedures are way to get IFR traffic from the airport to the en route system. There are four different procedures.
If an aircraft may turn in any direction from a runway within the limits of the assessment area and remain clear of obstacles that runway passes what is called a diverse departure assessment and no ODP is published.
There are a few in Kansas and Nebraska but  Florida, which is also pretty flat, only has a couple at military bases.
Obstacle Departure Procedures (ODP) are only used for obstruction clearance and do not include ATC related climb requirements. They often have higher visibility minimums and climb rates greater than 200 fpnm. Most are given as text, though occasionally there are graphical representations of them. They frequently have other restrictions, e.g. the tower must be open and monitoring a VOR, not available if local altimeter setting is not available. All but a few airports have an obstacle departure procedure.
A Standard Instrument Departure (SID) is an ATC-requested and developed departure route. Pilots must have at least the textual description of the procedure. SIDs always have a graphical depiction. Unlike Obstacle Departure Procedures, SIDs usually have portions where the altitude is restricted—either minimum or maximum. Most SIDs have multiple transitions to get you into the en route system. Small airports generally do not have SIDs and most airports that have scheduled air carrier service have at least one SID. While the primary purpose of a SID is to ease pilot and controller workload while getting the aircraft into the system, they also provide obstacle clearance.
A visual climb over airport (VCOA) is a departure option for an IFR aircraft, operating in VMC equal to or greater than the specified visibility and ceiling.
A radar departure is another option. They are established when ATC has a need to vector aircraft on departure to a particular ATS Route, NAVAID, or fix.
All departures (except VCOA) assume that the aircraft will cross the departure end of the runway at 35' or more, continue on the runway heading until reaching 400', and climb at a rate of 200 feet per nautical mile. Standard minimum visibility applies, 1 mile for 1 and 2 engines and ½ mile for 3+ engines.
You can read more about departure procedures in FAA-H-8083-16 Instrument Procedures Handbook, Chapter 1 Departures

Edited because I'm a moron and missed the intent of his question...
This gets deep into the weeds of Pt. 25 vs. Pt. 91 vs. Pt. 135/121.
First off, SIDs are intended for normal all-engine climb to transition from the terminal area into enroute airspace. They aren't specifically designed for obstacle avoidance though it is an important consideration. They don't account for obstacles within the first mile of the runway end, so just relying on SID gradient doesn't protect you against close-in obstacles.
I cribbed this from the FAA Instrument Flying Handbook regarding ODPs:

If an aircraft may turn in any direction from a runway within the
  limits of the assessment area and remain clear of obstacles that
  runway passes what is called a diverse departure assessment, and no
  ODP is published.

So ODPs can be created in conjunction with a SID if obstacles are a problem. "DUH" on my part...
Engine-out ODPs are created by individual operators (airlines etc) and intended only for use in an emergency: engine failure post-V1. It's easier if the engine-out path mirrors a SID, but it doesn't have to. Vertical obstacle clearance is less stringent than SID, but the 0.8% gross vs. net margin (assuming we're talking twin engine) provides a steadily increasing pad over distance.
SIDs/ODPs vs. engine-out ODPs is probably one of the most misunderstood subjects I've encountered in this business. The other is conflating "Climb" with "Obstacle Clearance" to mean the same thing, but there are subtle differences. I suspect both arise from instruction methods and rules of thumb that have evolved and been passed along over the years - if you're Joe Pilot with no access to an obstacle database, about the only recourse you have is to use the SID and hope there's nothing inside that first mile that you might hit (-ahem- MDW and TEB).

Why do you say that ODPs are "only for use in an emergency"? I'm fairly sure they aren't, and ATC can even assign them to you.

You may want to structure your post in paragraphs with blank lines.

Ah...I got you. I thought you meant engine-out ODPs.


text:
How to know what kinds of airfoil being used in a commercial propeller?
Suppose we know the 3D CAD model of a commercial propeller. Starting from that, we do the slicing to get the profile of airfoil being used to generate the complete shape of the propeller. How do we know the kinds of the airfoil from those section? Knowing there are thousands of airfoil profiles out of there, and we don't want to compare it one by one and mathcing the shape

Good reason to dig in and learn about how certain airfoil shapes give better L/D efficiency for a given range of AoA and rotation velocity.

Right! Airfoils distribution, twist distribution, and chord distribution all play their role in a propeller generation

You don't.
If you had a guess as to the family of airfoils -- and that family was parametrically defined -- you could write a program to do a nonlinear least squares fit of that family to your points.  However, if the airfoil was in-house or custom designed, then that would only find the closest airfoil in the family to the one that was used.  It probably isn't worth the trouble.
In the old days, most propellers used a Clark Y airfoil (along with everything else).  The NACA 16-series airfoil series was specifically developed for propellers.  The NACA 65-series airfoils are also frequently used on propellers.
If you have a CAD model that represents the foils accurately (often CAD models of propellers don't have real foil properties accurately represented) -- such that you can extract points and believe them, you should just use those points.
I assume you're after sectional aerodynamic data (lift, drag, moment) of the airfoils.  If you have high quality points, just perform a 2D analysis of the points and use your own computation.  That will work no matter the airfoil source.

Good point! I just feel curious whether we could somehow "decode" the propeller's airfoil being used and remake it with our own manufacturing capability

You could -- take the points from your slice and fit a smoothing spline to them.  You can use that curve without knowing where it came from (if the points are accurate).
If you really want to know where they came from, you can do the least squares fit to the airfoil family.  But what does knowing that the airfoil at mid-span was a NACA 16-408 get you vs. already having the curve and points?
If you really want to go down that path, I can help you more.  But you must decide if it is worth the hassle.

Oh I see.....I think the least square fit just enough for this case


text:
Are There Any Recomendation of Aircraft Design Books Written By Russian Author?
I've read many aircraft design books, such as the one written by Roskam (Vol 1-8), Raymer, and Torenbeek. I'm curious if there any aircraft design book written by any Russian author, which may they've used a different approach in accomplisihing the aircraft's DRO. If there any book recommendation, just let me know.
I've read many Russian aircraft history book written by Yefim Gordon, but the one I'm interested is in the design process (not the historical story).

This is not an answer, but there's a blog which lists public domain english translations of russian technical books, Mir Books. Their aerodynamics category might be of use to you. During the cold war, most of these titles would be translated by USFG so you can also see them on DTIC, but the blog collects a number of them.

While I can appreciate the reason for the close, it's not clear to me where else on stack exchange one might go to ask for books on Soviet era russian aircraft design.

An old book (1972 or so) is available from discover.dtic.mil Preliminary Design of an Aircraft, the dtic number is AD0741485.
Also, NASA translation AERODYNAMICS AND FLIGHT DYNAMICS OF TURBOJET AIRCRAFT published in 1969 may be of interest. It is on archive.org


text:
What valve would be the best for a model rocket with a hybrid engine?
I am planning on building a model rocket with a hybrid engine. I am trying to find the best valve that could be used for the MOV, main oxygen valve. I plan to use gaseous oxygen and would like the valve to be electrically actuated, and have the ability to throttle. Does anybody have any recommendations for a good valve to use? Thank you.

I think this question is better suited on space.SE

Technically, this cannot be a "model rocket" engine -- by legal definition, a model rocket uses only commercially made engines certified by either NAR or Tripoli Rocket Association (names may have changed in 20+ years I've been away from model rocketry).  This would be an "amateur rocket engine" and must meet a whole different set of legal requirements and insurance conditions.  Hint: you probably can't afford the insurance you should have to fly this anywhere other than Black Rock Desert or similar places.

@Zeissikon Thank you for the information.

It depends on a lot of factors.
Most valves with the specs you need will work really, but you'll have to carefully determine your specs. There's not really a single answer.
What kind of thrust are you designing your engine for? This (amongst other things) will determine your minimum needed flow rate, and will determine the pressures this valve will need to be able to cope with. These things will be the most important valve specs you'll be considering.
I don't know where exactly your valve will be in your engine, but make sure it can withstand the heat its exposed to.
On the flipside, knowing you'll be using GOX, you'll probably just use the pressure from your oxygen tank to power your engine. As the oxygen will be expanding, the MOV might tend to freeze up and lock itself in place. Beware of that as well when choosing a valve.
Not all valves will be able to safely operate in a pure oxygen environment. However, as we're talking model rockets here (the operating time of your engine is quite short I suppose) it'd surprise me if that would turn out to be an issue.
To end with, although maybe not directly related to your question about the valve, make sure you understand hybrid engine throttling. It can get more complicated than you might anticipate.

@PeterSmith Thank you for the help!


text:
My kid wants to be a pilot
My 7 yo is really keen on taking up aviation as a career.
I have seen multiple times where kids at the age of 15-16 get licenses to fly. How does that happen?
Looking for some advise on how to start this journey for my little man?

Assuming this is in the US, find a flight school, go on a discovery flight (yes, even at 7 years old). Be prepared to open your wallet. In the US you must be 16 to solo, but you can fly a glider solo at 14.

If you are in the US there is also the Civil Air Patrol in a few years.

There is also the Experimental Aircraft Association. They take kids as young a eight years old on a type of discovery flight so that they can get their first experiences in aviation through their Young Eagles program. They also give each participant access to a free online ground school. Flight training scholarships and internships are also available. https://youngeaglesday.org/

The following information is based on US FAA regulations and training programs.
In the US, there is no age limit (minimum or maximum) you must be in order to fly at the controls of an aircraft. There are age limits specified in Title 14 of the Code of Federal Regulations Part 61. Here are some of the particulars:

14 or older to solo a ballon or glider.
16 or older to get a balloon or glider private pilot certificate.
16 or older to solo a powered aircraft.
17 or older to get a powered aircraft private pilot certificate.
18 or older to get a commercial pilot certificate.

In the meantime, you can get your child into one of several youth aviation programs like Civil Air Patrol, or the Young Eagles.

Maybe start him with balsa/foam gliders that will help him learn about the basics of flight (lift, balance, etc). Toys are kid-friendly versions of things in the world, after all.

Here in the US, I have seen several kids solo in gliders at 14 years of age and get their private glider rating at 16 years of age.  Glider training is really good training.  Glider clubs vary wildly in terms of annual dues and rates for air time and tows.  Some are amazingly affordable, others are not.  Some have scholarships available to subsidize flight training for youth.  Commercial operations will always cost more, but require less investment in time.  Some research into what glider clubs are available to you within a reasonable driving distance, may really pay off.  There's not much point in starting this training more than a year or two before your son's 14th birthday.
When your kid is of an appropriate age, keep an eye out for any "Explorer" scout posts that exist in your area, with a focus on aviation.  Sometimes these units offer ground school courses, opportunities for flight experiences, etc.
Until then, in terms of just "stoking the fires" and exploring the general principles of flight, radio-controlled airplanes are great way to go, especially once your son gets to be around 11 to 13 years old.  The advent of airplanes made of EPP foam or other similar foams has brought about a whole new world in terms of crash-resistance and ease of repairs.  Don't start with something too exotic.  Something like the HobbyZone Super Cub is a great way to go.  It is very crashworthy due to its small size and light weight and mostly-solid-foam forward fuselage.  And many hobby stores carry individual parts such as motor, gearbox, wings, etc, for quick and inexpensive replacement.  The lack of ailerons are not a big issue-- you or your kid can always add them later.  Another way to go that might be suitable for a slightly younger age is a very light, small plane designed to fly indoors, such as the Eflite or Parkzone "Vapor".
Before then?  Some good books about aviation history with lots of well-done illustrations can help keep your kid's interest fired up.  Among other things, check out the Time-Life series called "The Epic of Flight".  These books were printed decades ago but still should be of interest.  They can often be found in second-hand book stores.  And yes, as some other answers and comments have noted, be sure to check out the Experimental Aircraft Association's "Young Eagles" program-- its whole purpose is to allow young people to experience flight in a light aircraft.


text:
Can Navy WSO use autopilot to fly to safety?
If pilot becomes incapacitated, can Navy WSO use autopilot to fly to a safe place to eject?

Does this answer your question? On the F15-E, can the WSO take over if the pilot is incapacitated?

Which aircraft? Some models have back seat controls, others (most for the USN) don't. The autopilot is not a taxi app with a home button, it just keeps the plane stable.

Not a dupe, for 2 reasons... the suggested question is all about the F-15E, while this question asks about Navy flying. Second, this question asks specifically about autopilot usage, which isn't addressed in the suggested question.

Reason for question: Ejecting in friendly territory at safe altitude is preferable, so do Navy WSO's have some means by which to climb, and bring the aircraft back to friendly territory, before ejecting crew? Only reason I've been given so far is that the pilot is rarely incapacitated, but given the seeming minimal expense of implementing a simple programmable autopilot, especially on fly-by-wire aircraft, why wouldn't the Navy want both crew members to have this capability?

Well, if he has flight controls, it'd be pretty easy to do that without an autopilot.


text:
What does the "High Alt Landing" guarded push button on the A320 exactly do?
I am aware that not all variants of the A320 are equipped with the HIGH ALT LANDING guarded push button. I know that it is pushed before landing at high altitude airfields. Was wondering what it does exactly?

Have you read this facebook post that suggests it's about affecting passenger oxygen masks?

@MrR Interesting did not come across that. Thanks for sharing!

The button raises the altitude at which the oxygen masks in the cabin automatically deploy. When landing at a high elevation airport, the masks might otherwise deploy during approach when the cabin pressure is reduced to the destination field pressure.

MASK MAN ON pb
The guard keeps this button in the AUTO position.
AUTO: The mask doors open automatically, when the cabin altitude exceeds 14 000 ft, or 16 000 ft if the HI ALT LANDING pb-sw is set to ON.
Pressed: The mask doors open.
HI ALT LANDING pb-sw
This pushbutton-switch changes the altitude threshold for the deployment of the passenger oxygen masks.
OFF: The masks drop, if the cabin pressure exceeds 14 000 ft (+ 250, -750 ft).
ON: The masks drop, if the cabin pressure exceeds 16 000 ft (+ 250, -750 ft).

(Airbus A320 FCOM - Oxygen - Fixed Oxygen System for Cabin - Controls and Indicators)

So this button would only be needed at La Paz, Bolivia and a handful of Chinese airports above 13,250ft?

@njuffa It isn't just the airport elevation. The approaches also have to be taken into account which are usually 2,000 feet above the surface.


text:
How to decide which aerodromes should have Electronic Terrain and Obstacle Data?

What is the meaning of "aerodrome that is regularly used in international civil aviation"?

Is there any explanation or reference material in support of Aeronautical Information System (AIS)?

I found several things in Eurocontrol document but there is no exact explanation and solution to decide which aerodromes should have Electronic Terrain and Obstacle database.

you need to check what is an aerodrome first which is basically small airport https://en.wikipedia.org/wiki/Aerodrome

@AtillaArdaAçıkgöz Aerodrome does not mean "small airport"; it is a general term covering everything from a tiny grass strip to the largest international airports.

@J.Hougaard that's true, shame on me i did not finished my sentence correctly. It was supposed to be "small airport to largest". At least that was what i had in my mind. shall i delete it or i could edit it, maybe?

Thanks for the replies, i should say, i'm looking for definition about "regularly used aerodromes in international civil aviation". This is a standard of ICAO that is key to select which aerodromes must have electronic terrain and obstacle database.                                            reference here: "From 12 November 2015, AT AERODROMES REGULARLY USED BY INTERNATIONAL CIVIL AVIATION, electronic obstacle data shall be provided for all obstacles within Area 2 that are assessed as being a hazard to air navigation.” ICAO ANNEX-15.

An aerodrome or airdrome is a location from which aircraft flight operations take place, regardless of whether they involve cargo, passengers, or military. Aerodromes include small general aviation airfields, large commercial airports, and military airbases.

An airport is an aerodrome with extended facilities, mostly for commercial air transport. Airports often have facilities to store and maintain aircraft, and a control tower. An airport consists of a landing area, which comprises an aerially accessible open space including at least one operationally active surface such as a runway for a plane to take off or a helipad, and often includes adjacent utility buildings such as control towers, hangars and terminals. Larger airports may have fixed-base operator services, airport aprons, taxiway bridges, air traffic control centers, passenger facilities such as restaurants and lounges, and emergency services.

With this definitions of aerodrome and airport from Wikipedia, we understand that all airports are aerodrome but not all aerodromes are airport i.e. airport is a subset of an aerodrome.
The Civil Aviation Safety Authority under CASR part 139 classifies the Aerodrome into below categories:

Certified Aerodromes
Registered Aerodromes
Other Aerodromes - more than 9 but not more than 30 passengers
Other Aerodromes - operations under proposed CASR part 135


text:
What is this large engine doing on a B52?
In this YouTube video, discussing plans to use the 747 as an aircraft carrier, there is a brief sequence starting at 4 min 14 s, showing images of a B52:

What is the explanation for the very different inboard engine pod on the starboard wing? There is a current call for proposals to re-engine the B52 with eight modern engines. Was this an earlier test of moving to four larger engines instead?

Wikipedia mentions that retrofitting the engines was considered in the 1970s and again in the 1980s, but I can't find a quotation that indicates it was physically tested.

You know, these days you could surely have a sort of "airborne drone aircraft carrier" - carrying a few dozen "big drones", say.  Unreal!

Testbed Aircraft Cameos

As a young engineer in the 1960s at Pratt & Whitney Aircraft (now
  UTC’s Pratt & Whitney) in East Hartford, Connecticut, I was involved
  (along with many others) in the development of their 44,000 pound
  thrust (lbt) JT9D turbojet, which powered the first Boeing 747 jumbo
  jet aircraft[ Display footnote number: 2 ]. Because of its then
  ground-breaking large fan diameter (new for the 1960s), P&WA had to
  use a U.S. Air Force Boeing B-52 as a testbed. The Stratofortress,
  with its high wing, allowed the JT9D to be mounted with adequate
  ground clearance for takeoff and landing. In Figure 1, the P&WA
  testbed aircraft is shown landing at the Windsor Locks, Bradley
  International Airport, after a test flight, with a JT9D engine
  replacing two TF-33 inboard engines on the right wing of the
  eight-engined B-52.
The B-52 continued as a P&WA testbed aircraft until 1981, even after
  being damaged in its hangar by a violent tornado that raced through
  Windsor Locks in 1979. Pratt & Whitney more recently used two Boeing
  747SP aircraft for testbeds, to flight test their new geared fan jet
  engines.

Thanks for a definitive answer and image. The rest of that post is worth looking at too. Will leave this open for a further feedback  but presumably this will be the answer I accept.

Dammit, beaten by just minutes :) points to you good sir for quicker fingers.

Does anyone happen to know the ultimate fate of JB-52E? Since it's a -E and the only ones in service today are -H I would assume it was either scrapped or boneyarded, but would love to know for certain.

FTR, the JT9D is a turbofan, not turbojet.

The plane in the pictures is Boeing JB-52E -test plane.
It used to test for instance the General Electric TF-39 engines for the C-5 Galaxy as it was under development

Nice - extends the other answer by showing that this was a testbed for several engine types.


text:
Why does the thrust limit page display the thrust in percentage (« % ») and not in pound-force?
When the pilot sets the takeoff engines thrust on the Flight Management thrust limit page that displays on the CDU (or MCDU) interface, the selection will finally show as a percentage.
The direct consequence of this is that, « at first sight », the pilot does not know the exact thrust that the engines will develop in pounds-force.
Considering that all operators do not necessarily choose the same rating for a similar combination of aircraft-engine, does it mean the same percentage of takeoff thrust might provide different thrusts according to the operator?


text:
In the last year, did Airbus make any changes to existing or newly built A220s control panels or AT/AP software?
As reported in various places (e.g. by simplyflying.com), there were two near-catastrophes in the A220, not because of the widely-discussed engine topic¹, but because of how autopilot & autothrottle works in combination with the fact that they're right next to each other on the control panel.
Both CAR and FAA responded by issuing their own EAD (PDF links: CAR's EAD, FAA's EAD) requiring an addition to the handbook to keep pilots from trying to engage either AP or AT too early. The FAA makes it very clear in their EAD they consider this only an interim measure.
My question is:

Have Airbus since changed anything to remedy the situation beyond the addition to the handbook? A hardware change to the control panel (such as moving on or both of the buttons) or a software change to the AP or AT features (such as refusing to engage below the 400ft limit mentioned by both EADs?
And if not, what are there in the way of rules, regulations or legislation to compel them to do so in a timely manner?

¹ (I'm writing this question after getting curious in the comments of that ASE question and being encouraged there to do so)

Yes, Airbus started to delivery the modifications to A220 in Q2 2024:

Inhibition of AP engagement until 6 seconds after takeoff
Autothrottle improvement to reduce probability of a disconnect during takeoff
Better warning messages

Source/Other infos: https://safetyfirst.airbus.com/inadvertent-autopilot-engagement-during-takeoff-on-a220-aircraft/


text:
EASA PPL theory instrumental approaches rules
I am learning for EASA PPL in Czech.
I noticed that in some of the books there is chapters about Instrumental Approaches Air Law rules.
For example -

ILS approaches
Parallel approaches
Simple Precision
Non-Precision Approach vs Precision Approach
Simple Approach systems vs Cat I, II//III systems
but in most of the PPL material that I saw, no one talking about these subjects.

should I know these subjects for PPL ?

In the USA IFR procedures are not expected to be known by VFR only private pilots.  If as you say the PPL material you are studying does not mention IFR approaches, what makes you think that EASA would require it?  Isn't the scope of PPL knowledge or requirements published somewhere?

It's exactly the probelm, I cant find anywhere the requirements of EASA PPL ...

Well, is it safe to presume you started here?  https://www.easa.europa.eu/domains/general-aviation/licensing-general-aviation


text:
Differences between CPL and PPL theories
I am learning now for EASA PPL exams in Czech.
I tried to find some question bank applications, and I found AviationExam app which looks very good.
the problem is that there is no PPL section in AviationExam, only CPL or ATPL.
How much CPL theory is harder than PPL theory ? Can I just use the CPL questions to prepare for PPL? or the theory is much harder ?

Probably you've solved this by now, but for EASA PPL there are the following options:
If it's Austro Control based question bank , https://aircademy.com/en/ecqb-ppl/ (look for ECQB-PPL TRAINING QUESTIONS download link below)
If it's the UK based Question Bank, then I've heard good things about https://www.airquiz.com/
Good Luck!


text:
How should I act after landing in big airport
So I have a PPL, in the time of my education I did some touch and goes in international airports, but never parked there.
I am planning now to fly to Dresden Airport from Prague, and I am a bit confused about how should I act after landing and arriving to the GA apron.
Is there anywhere I can read what to do?
How should I leave the airplane? Just take the keys?
How to exit the airport? How to come back? Should I do a security check when going back to the airplane?

Does Dresden require GA visitors to use a handling agent?

I don't know, how should I check it? Checked in jeppesen charts, didn't find something about handling agent

Personally I would act poor.

You need to follow all the local regulations from the aviation authority in the country in question. I can tell you what typical where I fly but this may vary. Most of the information for Dresden is listed here but in general:
You will likely be met by a marshaler who will show you where to park after you land and get taxi directions to your ramp of choice.
Typically transient GA planes are left locked, with the parking break off so that ground crews can move them about the ramp without you. Ive never left the keys to my plane with a ground crew and wouldn't even if asked. They dont need to get in my plane to move it. They will likely instruct you on what to do when you power down. The typical call out in the states is "parking break off?" before the marshaler drives away in his golf cart...
If you cross a border and need to clear customs you need to make sure that the airport in question has customs and then you will need to deal with any arrangements you may need to (including paperwork) before hand to make sure you can actually get cleared.
Most airports where I fly have some kind of an office/fixed base operations/management facility where you can physically exit the field (and it appears Dresden has a nice lounge). This is typically where you also pay for fuel and overnight parking. You will return through this facility as well. Again most major airports are open 24/7 (even GA facilities) but you should confirm this with them in advance if you intend on coming and going at odd hours.
You will not need to go through "security" in the typical airport sense to get back to your aircraft since you are using the private terminal. However as noted above you may need to organize some customs related things.
Also of note, if you are flying into a busy city airport they will expect you to be on top of your stuff. You may need to read back long taxi instructions, wait for a while on a taxi way for other flights to leave etc.

Here is a fascinating series of videos on flying into a country that has almost no GA support

As the Czech Republic and Germany are both Schengen member states, the OP will not need to clear customs. At this time there are also no special COVID-related entry requirements for Germany. There may be other requirements I'm not aware of though.

Good answer. I happened to land in Dresden a few weeks ago and park overnight. You will be met by a marshaller and guided to a parking position. Tiedown points exist on the tarmac and the marshaller will provide you with chocks and ropes if necessary, then drive you to the general aviation terminal. You just walk through a door into the arrival hall, maybe after telling the clerk's desk which aircraft you are and how long you will stay. On departure, you start with the door and clerk's desk again, pay your bill (expect 50€) and they will call a marshaller to pick you up. (@MeirTolpin)

Find out where the German AIS - Aeronautical Information Sevice is (google ais deutchland)
In AIS DE locate AIP - Aeronautical Information Publication
From AIP find section AD 2 AERODROMES

AD 2 Should have at least some of the information you need or instructions on who/what to contact for more info, also browse through the rest of the AIS for full understanding of operating in German airspace/aerodromes. You can always call the aerodrome and ask, contact info will be listed in AIP.
I'm hoping I've stated the obvious here, because the above is basic knowledge for PPL